In a media recording and reproducing device using a media disk, a turntable is fixed to a shaft of a spindle motor provided to the device, a disk is loaded and rotated on a disk loading surface of the turntable, and information is written and read out to and from the disk. The turntable having the media disk loaded thereon is rotated at high speed. Hence, when the loaded disk has a slight deviation or deflection with respect to an in-plane center of gravity, a rotation center of the disk in the plane is deviated due to a surface swinging. Therefore, an optical pickup of reading information from a track of the disk or recording information to a track of the disk is deviated from the track.
Hence, in order to further increase the jointing force of the rotating media disk, a following method has been suggested, for example. A central portion of the turntable is provided with an annular opening part, and the opening part is provided with a magnetic means. With the magnetic means, a clamper made of a magnetic metal thin plate such as iron plate provided to hold the loaded media disk is attracted. Accordingly, the media disk is strongly pressure-contacted in a direction of the disk loading surface of the turntable.
In general, since it is necessary to suppress rotational moment to the minimum, the turntable is made of a light synthetic resin. Also, regarding a structure of the magnetic means provided to the turntable, an annular magnet is fixed to the annular opening part of the central portion of the turntable or a back yoke made of a magnetic metal thin plate such as iron plate and an annular magnet are fixed.
Regarding the fixing method, the conventional method as shown in FIGS. 7 and 8 has been proposed (for example, refer to Patent Document 1). According to this conventional method, a plurality of protruding pawls 32 which are arranged to protrude from an outer peripheral edge of a back yoke 31 are integrally formed with the back yoke 31. Further, an outer peripheral wall of a ring-shaped opening part 34 at a central portion of a turntable part 33 is provided with vertical groove parts, horizontal groove parts and protrusion parts. The vertical groove parts are formed into a concave shape such that the protruding pawls 32 of the back yoke 31 can be fitted therein. The horizontal groove parts are notched into a substantial arc shape such that the protruding pawls 32 can rotate in the outer peripheral wall along a bottom surface of the opening part 34 from one sides of sidewall surfaces forming the vertical groove parts, respectively. The protrusion parts are provided in the vicinity of opening parts of the horizontal groove parts so as to regulate movement of the protruding pawls 32. Accordingly, the conventional method mechanically fixes the back yoke 31 to the turntable part 33.
However, in the above configuration, the back yoke 31 is simply mechanically fixed to the turntable part 33. Hence, the strength is insufficient and the back yoke 31 may be removed from the turntable part 33 due to the repetitive mounting and demounting of the clamper and the severe vibration and shock, so that the reliability is lowered.
Also, in order to improve the fixing strength between both members, it can be considered to use adhesive for the above configuration. However, when the back yoke 31 made of metal or clamp magnet 35 is adhered on the bottom surface of the ring-shaped opening part 34 of the turntable part 33 made of the synthetic resin, following problems are caused. That is, the synthetic resin has the considerably higher linear expansion coefficient than that of the metal or magnet. Hence, a considerable difference in the linear expansion coefficient occurs depending on a thermal condition of the using environment, so that the adhesion is forcibly detached and the back yoke 31 is removed from the adhesion part. Also, as time goes, the distortion is caused on the bottom surface of the ring-shaped opening part 34 of the turntable part 33 having the back yoke 31 adhered thereto, so that the adhesion is forcibly detached and the back yoke 31 is removed from the adhesion part.